Recent trends in dieting and healthy eating have shown a high demand for fresh produce. According to USDA Economic Research Service statistics, fresh spinach, for example, reached a record consumption in 2005 with 738 million pounds in the United States: more than 12 times the amount consumed in 1970. Processed spinach consumption, conversely, has tended to decline over the last few decades. This high demand for fresh, nutritious produce puts pressure on producers and processors to ensure that products are safe for human consumption, yet continue to retain expected nutritious and aesthetic qualities. Minimal processing and treatment appears desirable in order to maintain the fresh taste, texture, and nutrition of produce. However, many sources of contamination exist that can affect produce before, during, and after harvesting. Sources of contamination include fecal matter from animals, both wild and domestic, contaminated irrigation water, flooding of crops, as well as from personnel involved with handling of products
Due to the specific growth conditions of produce, particular varieties are not always in season locally, and are often shipped from all parts of the nation and world to meet the demands of consumers. Many aspects of shipping can cause a decrease in the quality of fresh produce. Spoilage could occur from, for example, unsanitary transportation vehicles, lengthy shipping schedules, and improper storage temperatures and ventilation of storage areas. Conventional methods of sanitizing fresh produce involve various washing procedures. More efficient processing methods are needed to reduce the risk of contaminated produce, while still maintaining its fresh qualities.
Atmospheric, non-equilibrium plasma (ANEP) is an example of a non-thermal processing method. There is a wide variance in the terminology for the process to produce such a plasma. In the literature, a variety of terminology is used to describe the phenomenon including atmospheric glow discharge, surface barrier discharge (SBD), dielectric barrier discharge (DBD), Single Dielectric Barrier Discharge (SDBD) and Surface Plasma Chemistry Process (SPCP). For convenience herein, the term dielectric barrier discharge (DBD) is used, without intending to exclude any of the ANEP plasma generating mechanisms implied by choosing a specific terminology for description of the technique herein.
FIG. 1 shows simplified examples of DBD configurations that may be used to produce an ANEP in an ambient air environment. A high voltage generator 10 applies an alternating current potential to a pair of metallic plates 20, 30, spaced apart from each other to form a region 50 in which an object may be placed. At least one dielectric layer 40 is disposed between a first plate 20 and the second plate 30. In this manner, the effect of the dielectric layer is to limit the current of any filamentary discharge that is formed between the plate 20, 30 so as to prevent the formation of a high current arc. The discharge in region 50 is thus limited in energy and results in an ANEP where variety of reactive species may be formed from the O2, N2 and possibly water vapor. FIG. 1A shows a configuration with one dielectric layer 40 laid against an electrode 20. FIG. 1B shows an example where a dielectric plate 40 is laid against an electrode 20 and another dielectric plate 60 is laid against a second electrode 30. The charge accumulation on the plates, which may be used in conjunction with the voltage waveform, to estimate the power consumption, may be measured by determining the voltage developed across a conventional capacitor 75. FIG. 1C illustrates a situation where a single dielectric layer 50 is disposed between the electrodes 20, 30, so that two regions 50 are formed in which an ANEP may be formed.
As the possibility of an arc forming directly between the plates 20, 30 exists, by air paths around the dielectric, at least one electrode is often fully enclosed in an insulating material, and the exposed electrode may be grounded. The insulating material may be the same material as used for the dielectric 40, 60 however the two materials may have differing properties. For example, the dielectric plate may be quartz, and the insulating material may be a moldable material.
The food industry is always seeking a better method for maintaining food safety and ozone treatment may be an effective possibility due to its antimicrobial properties and lack of residual substances. However, ensuring minimal to no exposure of employees to ozone is a concern. Similar considerations would apply to the medical field, where sterilizing packaged objects and maintaining sterile conditions is important.